Multifilamentary oxide superconducting wires and method of manufacturing the same

ABSTRACT

A multifilamentary oxide superconducting wire includes a metal matrix and a plurality of flat oxide superconductor filaments arranged in the metal matrix such that wide directions thereof are radially arranged in a section of the metal matrix. A method of manufacturing a multifilamentary oxide superconducting wire includes the steps of filling a raw material of an oxide superconductor in a through hole of a metal member to form a composite billet, subjecting the composite billet to a diameter reduction process to form a composite wire having a fan-like section, arranging composite wires so that larger arcs of the composite wires are located on the outer side, thus forming form a composite wire arrangement, covering the composite wire arrangement with a metal member to form a metal-covered composite wire arrangement, and performing a predetermined heating process of the metal-covered composite wire arrangement, thus forming the raw material into an oxide superconductor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a multifilamentary oxidesuperconducting wire having an excellent superconducting property, and amethod of efficiently obtaining such a multifilamentary oxidesuperconducting wire.

2. Description of the Related Art

Recently, Bi--Sr--Ca--Cu--O--, Y--Ba--Cu--O--, andTl--Ba--Ca--Cu--O-based oxide superconductors whose criticaltemperatures exceed the temperature of liquid nitrogen are found, andstudies on a variety of their applications are being made in variousfields.

These oxide superconductors are brittle. Hence, to form them into oxidesuperconducting wires having predetermined shapes, for example, a rawmaterial of an oxide superconductor is filled in a metal pipe to form acomposite billet, and the composite billet is subjected to a diameterreduction process to obtain a desired shape. When a predeterminedheating process is performed, the raw material is reacted to form anoxide superconductor, thereby obtaining a singlefilamentary oxidesuperconducting wire.

A multifilamentary oxide superconducting wire is manufactured in thefollowing manner. That is, a multiple of oxide superconducting wiresdescribed above are arranged in a metal pipe, subjected to a diameterreduction process to obtain a desired shape, and subjected to apredetermined heating process. Alternatively, a plurality of throughholes are formed in a metal billet, the raw material described above isfilled in the through holes to form a composite billet, and thecomposite billet is subjected to a diameter reduction process to obtaina desired shape, and subjected to a predetermined heating process.

However, these methods provide either a multifilamentary oxidesuperconducting wire in which oxide superconductor filaments 11 eachhaving a circular section are dispersed and composed in a metal matrix10, as shown in FIG. 1A, or a multifilamentary oxide superconductingwire in which oxide superconductor filaments 12 each having a flatrectangular section are aligned in a predetermined direction andcomposed in a metal matrix 10, as shown in FIG. 1B.

The former cannot obtain a high superconducting property since thepacking density of the oxide superconductor filaments 11 is low and thedegree of c-axis orientation of the superconductor is low. In thelatter, since the oxide superconductor filaments 12 each having the flatrectangular section are aligned only in the predetermined direction, theoxide superconductor filaments 12 become barriers against thermalconduction interfering with thermal conduction in the direction ofthickness. As a result, the cooling capability of the multifilamentaryoxide superconductor as a whole is decreased, and high superconductingproperty (such as critical temperature, critical current) cannot beobtained.

In the method of arranging multiple singlefilamentary oxidesuperconducting wires in the metal pipe, moreover it is difficult toalign the singlefilamentary oxide superconducting wires in the metalpipe, and some oxide superconductor filaments inevitably intersect witheach other in the obtained oxide superconductor. Since the intersectingportion is abnormally deformed, a high superconducting property cannotbe obtained.

The method of forming a plurality of through holes in the metal billetis not preferable since the hole forming operation requires much labor,especially when the number of holes is large.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a multifilamentaryoxide superconducting wire which exhibits an excellent superconductingproperty.

This object is further achieved by a multifilamentary oxidesuperconducting wire having a metal matrix and a plurality of flat oxidesuperconductor filaments arranged in the metal matrix such that widedirections thereof are radially arranged in a section of the metalmatrix.

This object is further achieved by multifilamentary oxidesuperconducting wire having a metal matrix and a plurality of fan-likesuperconducting filaments arranged in the metal matrix such that theirarcuated portions are on the outer side.

It is another object of the present invention to provide a method ofmanufacturing a multifilamentary oxide superconducting wire in which amultifilamentary oxide superconductor which exhibits an excellentsuperconducting property can be obtained.

This object is achieved by a method of manufacturing a multifilamentaryoxide superconducting wire having steps of filling a raw material of anoxide superconductor in a through hole of a metal member having thethrough hole to form a composite billet, subjecting the composite billetto a diameter reduction process to form a composite wire having a flator fanlike section, arranging the composite wires so that larger arcsthereof are located on the outer side, thus forming a composite wirearrangement, covering the composite wire arrangement with a metal memberto form a metal-covered arrangement, and performing a predeterminedheating process of the metal-covered arrangement to form the rawmaterial into an oxide superconductor.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention, and together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention.

FIGS. 1A to 1C are views showing sections of conventionalmultifilamentary oxide superconducting wires;

FIGS. 2A to 2F are views showing sections of multifilamentary oxidesuperconducting wires according to the present invention;

FIGS. 3A to 3G are views for explaining a method of manufacturing amultifilamentary oxide superconducting wire according to an embodimentof the present invention;

FIGS. 4A to 4C, 6A to 6H, 7A to 7C, and 11A to 11C are views forexplaining methods of manufacturing a multifilamentary oxidesuperconducting wires according to other embodiments of the presentinvention;

FIGS. 5A and 5B are views for explaining devices used for reducing thediameter of a composite wire in the present invention;

FIGS. 8A and 8B are views for explaining a method of manufacturing acomposite billet in the present invention; and

FIGS. 9A and 9B and 10A and 10B are views showing plate-like metalmembers used in the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Multifilamentary oxide superconducting wires according to the presentinvention will be described with reference to the accompanying drawings.

A multifilamentary oxide superconducting wire according to the presentinvention is obtained by arranging and composing oxide superconductorfilaments 21 each having a flat section in a metal matrix 20 such thattheir wide directions are radially arranged, as shown in FIG. 2A. Amultifilamentary oxide superconducting wire shown in FIG. 2B has oxidesuperconductor filaments 22 each having a fan-like section. with thisstructure, the area of the oxide superconductor filaments can beincreased in the section of the multifilamentary oxide superconductingwire, and a larger current can be supplied. A metal matrix 23 having arectangular section, as shown in FIG. 2C, can be used, a metal matrix 20having a hole 24 at its central portion for passing a refrigeranttherethrough, as shown in FIG. 2D or 2E, can be used, and a pluralityarray of flat oxide superconductor filament groups 26 concentricallyarranged such that their wide directions are radially arranged, as shownin FIG. 2F, can be formed.

In the present invention, copper, a copper alloy, silver, a silveralloy, and other metals having good thermal and electric conductivitiescan be used as a material of the metal matrix, and silver and a silveralloy having a good oxygen permeability can be preferably used.

Bi--, Y--, and Tl-based oxide superconductors can be used. As the rawmaterial of the oxide superconductor, in addition to an ordinary rawmaterial powder, an intermediate before forming an oxide superconductor,e.g., a calcined material, which is obtained by blending, mixing andcalcining primary material powders, as of an oxide and a carbonate,containing a constituent element of the oxide superconductor; acoprecipitated mixture obtained by mixing solutions of compoundscontaining a constituent element of the oxide superconductor to providea desired composition; an oxygendeficient composite oxide; and an alloyof a constituent element of the oxide superconductor can be used.

The section of the oxide superconductor filament can be of an arbitraryshape, e.g., a rectangle, a fan shape, and an elongated ellipse, and maypreferably be a flat shape so that the c-axis orientation of the crystalof the oxide superconductor is improved.

The section of the multifilamentary oxide superconducting wire is notlimited to a circle but can be a rectangle, an ellipse, or any otherarbitrary shape.

The present inventors have discovered that the flatter the section ofthe oxide superconductor filament, the better the c-axis orientation ofthe crystal of the oxide superconductor, and have reached the presentinvention.

In the oxide superconducting wire of the present invention, the c-axisorientation of the crystal of the oxide superconductor is improved by aflat oxide superconductor filament probably because of the followingreason. That is, when the raw material is heated to form an oxidesuperconductor, the crystal of the metal of the metal matrix has afunction to cause the crystal of the oxide superconductor to orientalong the c-axis. Thus, when the contact area of the oxidesuperconductor filament with the metal matrix is increased, thisfunction is enhanced.

A flatness L² /S (where L (mm) is a contact length of one oxidesuperconductor filament with the metal matrix in the section and S (mm²)is a sectional area of one oxide superconductor filament) indicating thedegree of flatness of an oxide superconductor layer is preferably 18 ormore in terms of the c-axis orientation. If the flatness is less than18, the c-axis orientation is insufficient to obtain thesuperconductivity.

In the oxide superconducting wire of the present invention, when theflat oxide superconductor filaments are arranged such that their widedirections are radially arranged, the thermal conductivity is increased.Generally, an oxide superconductor has a low thermal conductivity. Whenan oxide superconducting wire has a structure as shown in FIG. 1B,although the thermal conductivity in the widthwise direction is high,the thermal conductivity in the direction of thickness is low. As aresult, the cooling capability of the oxide superconductor as a whole isdecreased. Hence, when the oxide superconductor filaments are arrangedsuch that their wide directions are radially arranged, as in the presentinvention, heat is readily conducted without being interfered by theoxide superconductor filaments.

A method of manufacturing a multifilamentary oxide superconducting wireaccording to the present invention will be described.

First, a raw material 31 of an oxide superconductor is filled in a metalpipe 30 to form a composite billet 32, as shown in FIG. 3A. Then, thecomposite billet 32 is subjected to a diameter reduction process, thusforming a composite wire 33 having a fan-like section, as shown in FIG.3B. A plurality of composite wires 33 are arranged such that theirarcuated portions 33a are located on the outer side, thus forming acomposite wire arrangement 34, as shown in FIG. 3C. The composite wirearrangement 34 is arranged in a covering metal pipe 35 to form ametal-covered composite wire arrangement 36, as shown in FIG. 3D. Themetal-covered composite wire arrangement 36 or an arranged wire assembly37 shown in FIG. 3E obtained by subjecting the metal-covered compositewire arrangement 36 to a diameter reduction process is heated in apredetermined manner, thus obtaining a multifilamentary oxidesuperconducting wire 3 having oxide superconductor filaments 38 whosewide directions are radially arranged, as shown in FIG. 3F or 3G.

The composite billet described above is subjected to a diameterreduction process to form a composite wire 40 having a substantiallytrapezoidal section, as shown in FIG. 4A. A plurality of composite wires40 are arranged on a metal pipe 41 such that their arcuated portions areon the outer side, as shown in FIG. 4B, thus forming a composite wirearrangement 42. The composite wire arrangement 42 is set in a coveringmetal pipe 43 to form a metal-covered composite wire arrangement 44. Themetal-covered composite wire arrangement 44 is heated in a predeterminedmanner, thus obtaining a multifilamentary oxide superconducting wire 4having oxide superconductor filaments 45 whose wide directions areradially arranged and a hole portion 46 for passing a refrigeranttherethrough.

When the multifilamentary oxide superconducting wire is to bemanufactured in the above manner, composite wires each having a fan-likesection may be heated in a predetermined manner to cause the rawmaterial to react to form an oxide superconductor, and thereafter anarrangement may be formed, thus shortening the heating time. In thiscase, however, the arrangement must be treated carefully in thefollowing processes since the oxide superconductor filaments tend toeasily crack.

In the manufacturing method described above, since the composite wirearrangement is set in the covering metal pipe, not only the arrangementwire assembly is fixed but also the workability is improved. Other thansetting the composite wire arrangement in the covering metal pipe, thecomposite wire arrangement may be bound by a metal tape, or a metalmaterial may be formed on the surface of the composite wire arrangementby vapor deposition to cover it.

As a method of filling the raw material in the metal pipe, a powdery rawmaterial may be directly filled. Alternatively, a compact powderobtained by compacting a powdery raw material to have a predeterminedform in accordance with CIP (Cold Isostatic Pressing) or a sintered bodyof a compact powder may be filled.

In the manufacturing method of the present invention, to reduce thediameter of the composite billet in which the raw material is filled inthe metal pipe, normal methods including HIP (Hot Isostatic Pressing),extrusion, milling, drawing, swaging, and so on can be employed.

To reduce the diameter of the composite billet to form a composite wirehaving a fan-like section, after extrusion, the composite billet may bepressed by pressure rolls 50 having inclined shafts, as shown in FIG.5A, or by a mold 52 having a hole portion 51 having a fan-like section,as shown in FIG. 5B. Alternatively, conform extrusion may be employed.

Regarding conditions of the heating process for causing the raw materialof the oxide superconductor to react to form an oxide superconductor,the heating temperature is about 950° to 1,000° C. when thesuperconductor is a Y-based oxide superconductor, and is about 850° to1,000° C. when the superconductor is a Bi- and Tl-based oxidesuperconductor, heating being performed in an oxygen-containingatmosphere in either case.

In the method of the multifilamentary oxide superconducting wireaccording to the present invention, when a plate-like metal member 61having an array of through holes 60, as shown in FIG. 6A, is used, amultifilamentary oxide superconducting wire having an array of aplurality of stages of oxide superconductor filaments can bemanufactured.

This multifilamentary oxide superconducting wire manufacturing methodwill be described. A raw material 62 of the oxide superconductor isfilled in the through holes 60 of the plate-like metal member 61 shownin FIG. 6A to form a composite billet 63 shown in FIG. 6B. Thiscomposite billet 63 is subjected to a diameter reduction process to forma composite wire 64 having a fan-like section, as shown in FIG. 6C. Aplurality of composite wires 64 are assembled such that their arcuatedportions 64a are on the outer side, thus forming a composite wirearrangement 65, as shown in FIG. 6D. The composite wire arrangement 65is set in a covering metal pipe 66 to form a metal-covered compositewire arrangement 67, as shown in FIG. 6E. The metal-covered compositewire arrangement 67 or an arranged wire assembly 68 shown in FIG. 6Fobtained by subjecting the metal-covered composite wire arrangement 67to a diameter reduction process is heated in a predetermined manner,thus obtaining a multifilamentary oxide superconducting wire 6 havingconcentric oxide superconductor filaments 69 whose wide directions areradially arranged, as shown in FIG. 6G or 6H.

Alternatively, the composite billet described above is subjected to adiameter reduction process to form a composite wire 71 having asubstantially trapezoidal section and a plurality of through holes 70,as shown in FIG. 7A. A plurality of composite wires 71 are arranged on ametal pipe 72 such that their arcuated portions are on the outer side,as shown in FIG. 7B, thus forming a composite wire arrangement 73. Thecomposite wire arrangement 73 is set in a covering metal pipe 74, thusforming a metal-covered composite wire arrangement 75. The arrangement75 is heated in a predetermined manner, thus obtaining amultifilamentary oxide superconducting wire 7 having a plurality ofconcentric oxide superconductor filaments 76 whose wide directions areradially arranged and a hole portion 77 for passing a refrigeranttherethrough.

To form a composite billet, a plate-like metal member 81 having aplurality of grooves 80, as shown in FIG. 8A, may be prepared, a rawmaterial 82 may be filled in the grooves 80, and a metal lid 83 may beplaced on the plate-like metal member 81, as shown in FIG. 8B. Accordingto this method, the filling operation is facilitated, and the rawmaterial can be uniformly filled at a high density. When the rawmaterial 82 is continuously filled while the grooved plate-like metalmember 81 is caused to travel, a long composite billet can beefficiently manufactured.

A plate-like metal member 91 having a plurality of through holes 90formed in a plurality of arrays, as shown in FIG. 9A, may be used, and acomposite 92 having a plurality of arrays of raw material layers and afan-like section may be formed. When such a plate-like metal member 91is used, the number of steps of the diameter reduction process can bereduced, and the composite billet can be efficiently manufactured.

Furthermore, a plate-like metal member 101 in which a plurality ofthrough holes 100 are irregularly formed, as shown in FIG. 10A, may beused. With such a plate-like metal member 101, when a composite wire 102having a fan-like section is formed, as shown in FIG. 10B, the densityof the oxide superconductor can be increased.

In the multifilamentary oxide superconducting wire manufacturing methodaccording to the present invention, a plurality of through holes 111each having a flat section may be formed in a rod-like metal member 110serving as a metal matrix such that their wide directions are radiallyarranged, as shown in FIG. 11A. Then, a raw material 112 may be filledin the through holes 111 to form a composite billet 113, as shown inFIG. 11B. The composite billet 113 may be subjected to a diameterreduction process to form a composite wire 114. The composite wire 114may be heated in a predetermined manner, thereby multifilamentary oxidesuperconducting wire.

EXAMPLE 1

Bi₂ O₃, SrCO₃, CaCO₃, and CuO powders were blended such that Bi: Sr: Ca:Cu was 2:2:1:2 in an atomic ratio, mixed, calcined in an outer air at820° C. for 50 hours, and pulverized to form a calcined powder having anaverage particle size of 5 μm.

The calcined powder was compacted and subjected to the CIP process toform a rod having a diameter of 15 mm. The rod was set in an Ag pipehaving outer and inner diameters of 25 and 15 mm, respectively, thusforming a composite billet. The composite billet was extruded, thusobtaining a composite wire having a fan-like section with one arc of 0.2mm, the other arc of 1 mm, and a width of 5 mm. This composite wire wasfinished using the mold shown in FIG. 5B.

A desired number of thus-obtained composite wires were arranged suchthat their larger arcs were located on the outer side to form acomposite wire arrangement. An Ag tape having a thickness of 0.2 mm waswound on the circumferential surface of the composite wire arrangement,thus forming an Ag-covered composite wire arrangement.

Then, the Ag-covered arrangement was heated at 850° C. for 50 hours in astream of oxygen, thus forming a multifilamentary oxide superconductingwire having a section shown in FIG. 3F.

EXAMPLE 2

A calcined powder obtained as in Example 1 was compacted and subjectedto the CIP process to form a rod having a diameter of 15 mm. The rod wasset in an Ag pipe having outer and inner diameters of 25 and 15 mm,respectively, thus forming a composite billet. The composite billet wasswaged and extruded to form a wire. The wire was pressed using the moldshown in FIG. 5B, thus obtaining a composite wire having a fan-likesection with one arc of 1 mm, the other arc of 2 mm, and a width of 5mm.

A desired number of thus-obtained composite wires were arranged on an Agpipe having outer and inner diameters of 10 and 6 mm, respectively, suchthat their larger arcs were located on the outer side to form acomposite wire arrangement. An Ag tape having a thickness of 0.2 mm waswound on the circumferential surface of the composite wire arrangement,thus forming an Ag-covered composite wire arrangement.

Then, the Ag-covered composite wire arrangement was heated at 850° C.for 50 hours in a stream of oxygen, thus forming a multifilamentaryoxide superconducting wire having a section shown in FIG. 4C.

EXAMPLE 3

An Ag pipe having a thickness of 2 mm was fitted on a composite wirearrangement obtained as in Example 1 to form a metal-covered compositewire arrangement. The metal-covered composite wire arrangement wasswaged to form an arranged wire assembly having an outer diameter of 8mm. This assembly was heated at 850° C. for 50 hours in a stream ofoxygen, thus forming a multifilamentary oxide superconducting wirehaving a section shown in FIG. 3G.

EXAMPLE 4

A multifilamentary oxide superconducting wire having a section shown inFIG. 4C was manufactured by following the same procedures as in Example2 except that a calcined powder having an average particle size of 5 μm,which had been obtained by blending Bi₂ O₃, PbO, SrCO₃, CaCO₃, and CuOpowders such that Bi: Pb: Sr: Ca: Cu was 1.6:0.4:2:2:3 in an atomicratio, mixing, calcining in an outer air at 750° C. for 50 hours, andpulverizing, was used.

Control 1

A calcined powder obtained as in Example 1 was compacted and subjectedto the CIP process to obtain a rod having a diameter of 20 mm. An Ag rodhaving an outer diameter of 100 mm and seven through holes formed at thesame pitch and each having an outer diameter of 20 mm was prepared.Seven rods thus obtained were inserted in the through holes of the Agrod to form a composite billet. The composite billet was swaged andheated following the same procedures as in Example 1, thus forming amultifilamentary oxide superconducting wire having an outer diameter of10 mm and a section shown in FIG. 1A.

Control 2

A calcined powder obtained as in Example 2 was compacted and subjectedto the CIP process to form a rod having a diameter of 12 mm. This rodwas set in an Ag pipe having outer and inner diameters of 20 and 12 mm,respectively. The obtained structure was swaged and milled to form atape-like rectangular wire having a width of 5 mm and a thickness of 0.2mm.

A plurality of tape-like wires thus obtained were aligned in a square Agpipe having outer and inner sides of 40 and 30 mm, respectively, to forma composite billet. This composite billet was milled to form amultifilamentary oxide superconducting wire having a thickness of 4 mmand a width of 18 mm.

This multifilamentary oxide superconducting wire was heated followingthe same procedures as in Example 2, thus forming a multifilamentaryoxide superconducting wire having a section shown in FIG. 1B.

The critical temperature (Tc) and the critical current density (Jc) in aliquid nitrogen of each of the multifilamentary oxide superconductingwires manufactured in Examples 1 to 4 and Controls 1 and 2 were measuredin normal measuring methods. Table 1 shows the results.

                  TABLE 1                                                         ______________________________________                                                      Section of                                                                    Multifila-                                                      Type of       mentary oxide                                                   Super-        superconduct-                                                   conductor     ing wire     Tc (K)  Jc (A/cm.sup.2)                            ______________________________________                                        Example 1                                                                             Bi-based  FIG. 3F      88    7,500                                    Example 2                                                                             Bi-based  FIG. 4C      90    8,380                                    Example 3                                                                             Bi-based  FIG. 3G      92    8,750                                    Example 4                                                                             Bi-Pb-based                                                                             FIG. 4C      95    9,800                                    Control 1                                                                             Bi-based  FIG. 1A      82    1,100                                    Control 2                                                                             Bi-based  FIG. 1B      90    3,500                                    ______________________________________                                    

As is apparent from Table 1, the multifilamentary oxide superconductingwires of Examples 1 to 4 had large Tc and Jc values. In particular, thesuperconductor of Example 2 exhibited an excellent superconductingproperty as cooling was promoted inside the superconductor. In thesuperconductor of Example 3, since the metal-covered arrangement wassubjected to diameter reduction process, the adhesion strength of thecomposite wires was increased to enhance the cooling effect, thusexhibiting an excellent superconducting property.

In contrast to these, in Control 1, since the oxide superconductorfilaments had a circular section, the density of the oxidesuperconductors was low to degrade the superconducting property. InControl 2, since the oxide superconductor filaments interfered withthermal conduction in the direction of thickness, the cooling effect waslow. Jc values were small in both Controls 1 and 2.

EXAMPLE 5

Bi₂ O₃, SrCO₃, CaCO₃, and CuO powders were blended such that Bi: Sr: Ca:Cu was 2:2:1:2 in an atomic ratio, mixed, calcined in an outer air at820×C for 50 hours, and pulverized to form a calcined powder having anaverage particle size of 5 μm.

The calcined powder was compacted and subjected to the CIP process toform a rod having a size of 2 mm×2 mm. An Ag pipe in which three throughholes each having a size of 2 mm×2 mm were formed in an array and whichhas an thickness of 4 mm and a width of 10 mm was prepared. Rods thusobtained were filled in the through holes of this Ag pipe, thus forminga composite billet. The composite billet was extruded, thus obtaining acomposite wire having a fan-like section with one arc of 0.2 mm, theother arc of 2 mm, and a width of 10 mm. The composite wire was finishedusing the milling rolls shown in FIG. 5A.

A desired number of thus-obtained composite wires were arranged suchthat their larger arcs were located on the outer side to form acomposite wire arrangement. An Ag tape having a thickness of 0.2 mm waswound on the circumferential surface of the composite wire arrangement,thus forming an Ag-covered composite wire arrangement.

Then, the Ag-covered composite wire arrangement was heated at 850° C.for 50 hours in a stream of oxygen, thus forming a multifilamentaryoxide superconducting wire having a section shown in FIG. 6D.

EXAMPLE 6

An Ag pipe in which three through holes each having a size of 2 mm×2 mmwere formed in an array and which had an outer diameter of 4 mm and alength of 8 mm was prepared. Rods manufactured as in Example 5 werefilled in the through holes of the Ag pipe, thus forming a compositebillet. The composite billet was extruded and pressed using the moldshown in FIG. 5B, thus obtaining a composite wire having a fan-likesection with one arc of 0.7 mm, the other arc of 2 mm, and a width of 8mm.

A desired number of thus-obtained composite wires were arranged on an Agpipe having outer and inner diameters of 8 and 6 mm, respectively, suchthat their larger arcs were located on the outer side to form acomposite wire arrangement. An Ag tape having a thickness of 0.2 mm waswound on the circumferential surface of the composite wire arrangement,thus forming an Ag-covered composite wire arrangement.

Then, the Ag-covered composite wire arrangement was heated at 825° C.for 50 hours in an outer atmosphere, thus forming a multifilamentaryoxide superconducting wire having a section shown in FIG. 7C.

EXAMPLE 7

An Ag pipe having a thickness of 2 mm was fitted on a composite wirearrangement obtained as in Example 5 to form an Ag-covered compositewire arrangement. The Ag-covered composite wire arrangement was swagedto form an arranged wire assembly having an outer diameter of 8 mm. Thisassembly was heated at 850° C. for 50 hours in a stream of oxygen, thusforming a multifilamentary oxide superconducting wire having a sectionshown in FIG. 6H.

EXAMPLE 8

A multifilamentary oxide superconducting wire having a section shown inFIG. 7C was manufactured by following the same procedures as in Example6 except that a calcined powder having an average particle size of 5 μm,which had been obtained by blending Bi₂ O₃, PbO, SrCO₃, CaCO₃, and CuOpowders such that Bi: Pb: Sr: Ca: Cu was 1.6:0.4:2:2:3 in an atomicratio, mixing, calcining in an outer air at 750° C. for 50 hours, andpulverizing, was used.

Control 3

A calcined powder obtained as in Example 5 was compacted and subjectedto the CIP process to obtain a rod having a diameter of 20 mm. An Ag rodhaving an outer diameter of 100 mm and seven through holes formed at thesame pitch and each having an outer diameter of 20 mm was prepared.Seven rods thus obtained were inserted in the through holes of the Agrod to form a composite billet. The composite billet was swaged andheated following the same procedures as in Example 5, thus forming amultifilamentary oxide superconducting wire having a section shown inFIG. 1A.

Control 4

A calcined powder obtained as in Example 5 was compacted and subjectedto the CIP process to form a rod having a diameter of 12 mm. This rodwas filled in an Ag pipe having outer and inner diameters of 20 and 12mm, respectively. The obtained structure was swaged and milled to form asinglefilamentary oxide superconducting wire having an outer diameter of1 mm. A plurality of oxide superconducting wires thus obtained wereinserted in an Ag pipe having outer and inner sides of 34 mm and 26 mm,respectively, thus forming a composite billet. The composite billet wasmilled to form a multifilamentary oxide superconducting wire having anouter diameter of 20 mm.

This multifilamentary oxide superconducting wire was heated followingthe same procedures as in Example 5, thus forming a multifilamentaryoxide superconducting wire having a section shown in FIG. 1C. That is,in the section of this multifilamentary oxide superconducting wire,oxide superconductor filaments 11 were dispersed in a metal matrix 10.

The critical temperature (Tc) and the critical current density (Jc) in aliquid nitrogen of each of the multifilamentary oxide superconductingwires manufactured in Examples 5 to 8 and Controls 3 and 4 weremeasured. Table 2 shows the results together with the number of oxidesuperconductor filaments, i.e., the number of cores.

                  TABLE 2                                                         ______________________________________                                                     Section of                                                                    Multifila-                                                       Type of      mentary ox-        Num-                                          Super-       oxide super-       ber                                           con-         conduct-           of    Jc                                      ductor       ing wire   Tc(K)   Cores (A/cm.sup.2)                            ______________________________________                                        Example 5                                                                             Bi-based FIG. 6D    88    102   7,500                                 Example 6                                                                             Bi-based FIG. 7C    90    69    8,380                                 Example 7                                                                             Bi-based FIG. 6H    92    93    8,750                                 Example 8                                                                             Bi-Pb-   FIG. 7C    95    69    9,800                                         based                                                                 Control 3                                                                             Bi-based FIG. 1A    82     7    1,100                                 Control 4                                                                             Bi-based FIG. 1B    90    80    3,500                                 ______________________________________                                    

As is apparent from Table 2, the multifilamentary oxide superconductingwires of Examples 5 to 8 had large Tc and Jc values. In particular, thesuperconductor of Example 6 exhibited an excellent superconductingproperty as cooling was promoted inside the superconductor. In thesuperconductor of Example 7, since the metal-covered arrangement wassubjected to diameter reduction process, the adhesion strength of thecomposite wires was increased to enhance the cooling effect, thusexhibiting an excellent superconducting property.

In contrast to these, in Control 3, since the oxide superconductorfilaments had a circular section and thus provided a large area with asmall number of cores, the density of the oxide superconductors was lowto degrade the superconducting property. In Control 4, since thesinglefilamentary oxide superconducting wires were inserted in metalpipes in a one-to-one correspondence to provide a multifilamentary oxidesuperconducting wire, the wires locally intersected with each other. Theintersecting portions were abnormally deformed. Jc values were small inboth Controls 3 and 4.

EXAMPLE 9

Bi₂ O₃, SrCO₃, CaCO₃, and CuO powders were blended such that Bi: Sr: Ca:Cu was 2:2:1:2 in an atomic ratio, mixed, calcined in an outer air at820° C. for 50 hours, and pulverized to form a calcined powder.

The calcined powder was compacted and subjected to the CIP process toform a desired number of compacted bodies each having a rectangularsection, a width of 10 mm, and a different thickness, i.e., a differentflatness. Through holes each having the same section as that of eachcompacted body were formed in an Ag pipe having an outer diameter of 30mm such that their wide directions were radially arranged. The compactedbodies were inserted in the through holes, thus forming a compositebillet. The number of through holes was adjusted such that the totalsectional area of the through holes was identical in all compositebillets.

The composite billet was swaged to form an oxide superconducting wirehaving an outer diameter of 2 mm. The oxide superconducting wire washeated at 850° C. for 50 hours in a stream of oxygen, thus forming amultifilamentary oxide superconducting wire having the same section asthat shown in FIG. 2A.

EXAMPLE 10

A desired number of compacted bodies each having a rectangular section,a width of 10 mm, and a different thickness, i.e., a different flatnesswere formed by compacting and performing the CIP process of the calcinedpowder obtained as in Example 9. Through holes each having the samesection as that of each compacted body were formed in an Ag pipe havingouter and inner diameters of 30 mm and 5 mm such that their longitudinaldirections were radially arranged. The compacted bodies were inserted inthe through holes, thus forming a composite billet. The number ofthrough holes was adjusted such that the total sectional area of thethrough holes was identical in all composite billets.

The composite billet was swaged to form a multifilamentary oxidesuperconducting wire having an outer diameter of 10 mm. The oxidesuperconducting wire was heated at 850° C. for 50 hours in a stream ofoxygen, thus forming a multifilamentary oxide superconducting wirehaving the same section as that shown in FIG. 2E.

EXAMPLE 11

A multifilamentary oxide superconducting wire having a section shown inFIG. 2E was manufactured by following the same procedures as in Example10 except that a calcined powder having an average particle size of 5μm, which had been obtained by blending Bi₂ O₃, PbO, SrCO₃, CaCO₃, andCuO powders such that Bi: Pb: Sr: Ca: Cu was 1.6:0.4:2:2:3 in an atomicratio, mixing, calcining in an outer air at 750° C. for 50 hours, andpulverizing, was used.

CONTROL 5

A calcined powder obtained as in Example 9 was compacted and subjectedto the CIP process to obtain a rod having a diameter 5 mm. An Ag rodhaving an outer diameter of 25 mm and seven through holes formed at thesame pitch and each having an outer diameter of 5 mm was prepared. Sevenrods thus obtained were inserted in the through holes of the Ag rod barto form a composite billet. The composite billet was swaged and heatedfollowing the same procedures as in Example 9, thus forming amultifilamentary oxide superconducting wire having an outer diameter of2 mm and a section shown in FIG. 1A.

CONTROL 6

A calcined powder obtained as in Example 10 was compacted and subjectedto the CIP process to form a rod having a diameter of 12 mm. This rodwas set in an Ag pipe having outer and inner diameters of 20 and 12 mm,respectively. The obtained structure was swaged and milled to form atape-like wire having a rectangular section, a width of 5 mm, and athickness of 0.2 mm.

A plurality of tape-like wires thus obtained were inserted in a squareAg pipe having outer and inner sides of 40 mm and 30 mm, respectively,thus forming a composite billet. The composite billet was milled to forma multifilamentary oxide superconducting wire having a thickness of 1 mmand a width of 3 mm.

This multifilamentary oxide superconducting wire was heated followingthe same procedures as in Example 10, thus forming a multifilamentaryoxide superconducting wire having a section shown in FIG. 1B.

The critical temperature (Tc) and the critical current density (Jc) in aliquid nitrogen of each of the multifilamentary oxide superconductingwires manufactured in Examples 9 to 11 and Controls 5 and 6 weremeasured in normal measuring methods. Table 3 shows the results.

                  TABLE 3                                                         ______________________________________                                        Type       Section of  Flatness                                               of         Multifila-  of Super-                                              Super-     mentary oxide                                                                             conductor                                              con-       superconduct-                                                                             filament  Tc   Jc                                      ductor     ing wire    (L.sup.2 /S)                                                                            (K)  (A/cm.sup.2)                            ______________________________________                                        Example                                                                              Bi-     FIG. 2A     88      91   8,380                                 9      based                                                                         Bi-     FIG. 2A     48      90   7,500                                        based                                                                         Bi-     FIG. 2A     32      89   7,250                                        based                                                                         Bi-     FIG. 2A     20      89   6,000                                        based                                                                  Example                                                                              Bi-     FIG. 2E     62      92   8,750                                 10     based                                                                         Bi-     FIG. 2E     45      91   7,750                                        based                                                                         Bi-     FIG. 2E     33      90   7,500                                        based                                                                         Bi-     FIG. 2E     18      89   6,100                                        based                                                                  Example                                                                              Bi-     FIG. 2E     45      95   10,000                                11     based                                                                  Control 5                                                                            Bi-     Fig. 1A     13      82   1,100                                        based                                                                  Control 6                                                                            Bi-     Fig. 1B     45      89   3,600                                        based                                                                  ______________________________________                                    

As is apparent from Table 3, the multifilamentary oxide superconductingwires of Examples 9 to 11 had large Tc and Jc values.

In contrast to these, in Control 5, since the oxide superconductorfilaments had a circular section, its crystal had poor c-axisorientation. In Control 6, since the oxide superconductor filamentsinterfered with thermal conduction in the direction of thickness, thecooling effect was low, and the Jc value was small.

EXAMPLE 12

Y₂ O₃, BaCO₃, and CuO powders were blended such that Y: Ba: Cu was 1:2:3in an atomic ratio, mixed, calcined in an outer air at 900° C. for 100hours, and pulverized to form a calcined powder having an averageparticle size of 5 μm.

The calcined powder was compacted and subjected to the CIP process toform a desired number of compacted bodies each having a rectangularsection, a width of 10 mm, and a different thickness, i.e., a differentflatness. Through holes each having the same section as that of eachcompacted body were formed in an Ag pipe having an outer diameter of 30mm such that their wide directions were radially arranged. The compactedbodies were inserted in the through holes, thus forming a compositebillet. The number of through holes was adjusted such that the totalsectional area of the through holes was identical in all compositebillets.

The composite billet was swaged and milled to form an oxidesuperconducting wire having an outer diameter of 2 mm. The oxidesuperconducting wire was heated at 920° C. for 20 hours in a stream ofoxygen, thus forming a multifilamentary oxide superconducting wirehaving the same section as that shown in FIG. 2A.

EXAMPLE 13

A multifilamentary oxide superconducting wire having a section shown inFIG. 2A was manufactured by following the same procedures as in Example12 except that a calcined powder having an average particle size of 5μm, which had been obtained by blending Tl₂ O₃, BaCO₃, CaCO₃, and CuOpowders such that Tl: Ba: Ca: Cu was 2:2:2:3 in an atomic ratio, mixing,calcining in an outer air at 750° C. for 20 hours, and pulverizing, wasused. In this case, the heat treatment is performed under a condition of850° C.×50 hours.

CONTROL 7

A calcined powder obtained as in Example 12 was compacted and subjectedto the CIP process to obtain a rod having a diameter 5 mm. An Ag rodhaving an outer diameter of 25 mm and seven through holes formed at thesame pitch and each having an outer diameter of 5 mm was prepared. Sevenrods thus obtained were inserted in the through holes of the Ag rod toform a composite billet. The composite billet was swaged and heatedfollowing the same procedures as in Example 12, thus forming amultifilamentary oxide superconducting wire having an outer diameter of2 mm and a section shown in FIG. 1A.

CONTROL 8

A calcined powder obtained as in Example 13 was compacted and subjectedto the CIP process to obtain a rod having a diameter 5 mm. An Ag rodhaving an outer diameter of 25 mm and seven through holes formed at thesame pitch and each having an outer diameter of 5 mm was prepared. Sevenrods thus obtained were inserted in the through holes of the Ag rod toform a composite billet. The composite billet was swaged and heatedfollowing the same procedures as in Example 12, thus forming amultifilamentary oxide superconducting wire having an outer diameter of2 mm and a section shown in FIG. 1A.

The critical temperature (Tc) and the critical current density (Jc) in aliquid nitrogen of each of the multifilamentary oxide superconductingwires manufactured in Examples 12 and 13 and Controls 7 and 8 weremeasured in normal measuring methods. Table 4 shows the results.

                  TABLE 4                                                         ______________________________________                                        Type       Section of  Flatness                                               of         Multifila-  of Super-                                              Super-     mentary oxide                                                                             conductor                                              con-       superconduct-                                                                             filament  Tc   Jc                                      ductor     ing wire    (L2/S)    (K)  (A/cm.sup.2)                            ______________________________________                                        Example                                                                              Y-      FIG. 2A     89       91  2,930                                 12     based                                                                         Y-      FIG. 2A     50       92  2,850                                        based                                                                         Y-      FIG. 2A     35       90  2,900                                        based                                                                         Y-      FIG. 2A     20       89  2,500                                        based                                                                  Example                                                                              Tl-     FIG. 2A     65      110  13,600                                13     based                                                                         Tl-     FIG. 2A     42      115  12,100                                       based                                                                         Tl-     FIG. 2A     34      112  12,000                                       based                                                                         Tl-     FIG. 2A     18      110  8,500                                        based                                                                  Control 7                                                                            Y-      FIG. 1A     13       88    850                                        based                                                                  Control 8                                                                            Tl-     FIG. 1A     13      108  3,400                                        based                                                                  ______________________________________                                    

As is apparent from Table 4, the multifilamentary oxide superconductingwires of Examples 12 and 13 had large Tc and Jc values.

In contrast to these, in Control 5, since the oxide superconductorfilaments had a circular section, its crystal had poor c-axisorientation.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details, representative devices, andillustrated examples shown and described herein. Accordingly, variousmodifications may be made without departing from the spirit or scope ofthe general inventive concept as defined by the appended claims andtheir equivalents.

What is claimed is:
 1. A multifilamentary oxide superconducting wire,comprising a metal matrix and a plurality of oxide superconductorfilaments each having an oblong cross section and arranged in said metalmatrix such that a longer side of said oblong cross section extends in aradial direction of the oxide superconducting wire, wherein said oxidesuperconductor filaments have a flatness (L² /S) of not less than 18,where L (mm) is a peripheral length in cross section of the oxidesuperconductor filaments, and S (mm²) is a cross sectional area of theoxide superconductor filaments.
 2. The superconducting wire according toclaim 1, wherein said oxide superconductor filaments are arranged toform a plurality of arrays concentric with each other.
 3. Thesuperconducting wire according to claim 2, wherein said oxidesuperconductor filaments in each of the composite wires are arranged ina non-linear configuration.
 4. The superconducting wire according toclaim 1, wherein said oxide superconductor filaments have a crosssectional shape selected from the group consisting of a rectangularshape, a polygonal shape, an elliptical shape and a fan-like shape. 5.The superconducting wire according to claim 1, wherein said metal matrixis interposed between a metal pipe and said outer layer.
 6. Thesuperconducting wire according to claim 1, wherein said oxidesuperconductor is formed of a material selected from the groupconsisting of a Y-based material, a Bi-based material, and a Tl-basedmaterial.